KR20030077975A - Method for removing organic pollutants in fly ash - Google Patents

Abstract

The method of minimizing the concentration of harmful organic compounds in the fly ash of a combustion plant is such that when certain combustion conditions are identified that cause organic pollutants, especially dioxins and / or furans or precursors of dioxins and / or furans, the compounds decompose. The fly ash generated in the combustion plant is circulated to the combustion process so as to be possible.

Description

How to remove organic pollutants in fly ash {METHOD FOR REMOVING ORGANIC POLLUTANTS IN FLY ASH}

The present invention relates to a method for minimizing the concentration of toxic organic pollutants in fly ash in a combustion plant, in particular a waste incinerator apparatus, which circulates at least a portion of the fly ash generated in the incinerator into the combustion process.

Toxic organic pollutants in fly ash include, in particular, polychlorinated dibenzodioxin (PCDDs), polychlorinated dibenzofuran (PCDFs), precursors of PCDDs and PCDFs, namely monochlorobenzene, polychlorinated biphenyls (PCBs), and There are other compounds with equivalent structure or effect. The organic pollutants are often disclosed and quantified in the literature and emission regulations by the internationally adopted toxic equivalents (ng I-TEQ / kg), denoted ng / kg non-repeated. I-TEQ is the total equivalent toxicity (international toxic equivalent) of a number of organic pollutants to Seveso dioxin (2, 3, 7, 8-tetrachlorodibenzodioxin).

EP 0 862 019 A1 discloses vitrifying and sintering fly ash by circulating at least a portion of fly ash from the combustion plant into the hot zone of the combustion plant. The product obtained in this way can be added back to the grate ash or used separately. As a result, the residual amount of fly ash can be reduced. The fly ash is removed by cleaning the boiler or by stripping it from the filter device and then fed back to the furnace above the fuel bed when a grate based combustion system is used. This method did not consider the presence of harmful compounds such as dioxins and precursors of these dioxins.

In DE 33 20 466 C3, the ash ash is circulated back to the combustion chamber of the combustion plant. This fly ash is chemically treated outside the combustion chamber before it is circulated, the purpose of which is to reduce pollutants. Thus, a small portion of contaminants during fly ash are returned from the high temperature process and incorporated into the bottom ash.

It is an object of the present invention that organic pollutants in fly ash are controlled, in which most of the precursors or other organic pollutants are destroyed, thereby controlling the circulation of ash ash in the combustion process to minimize the amount of harmful organic compounds exiting the combustion plant with fly ash. It is to provide a method of removing the substance.

In order to achieve the above object, the present invention is characterized in that it performs a fly ash cycle as a function of specific combustion conditions in which organic pollutants such as PCDDs or PCDFs or precursor materials (precursors of PCDDs or PCDFs) are produced at high levels. do.

1 is a flow chart briefly and exemplarily illustrating a method for removing organic pollutants in fly ash according to the present invention.

According to the process for removing organic pollutants in fly ash according to the present invention, fly ash is removed when a certain combustion condition increases the amount of precursor material or other harmful organic pollutants that should be minimized as much as possible. This is an important feature of the present invention because the precursor material on the contact surface at a predetermined temperature, eg 200-400 ° C., downstream of the steam generator (boiler) remains attached or in particular copper, soot, And conversion to dioxins and / or furans in the presence of chlorine. This conversion reaction can occur within minutes to hours, and the exact time depends on the overall temperature conditions and the concentrations of materials such as copper, chlorine, and soot that act as catalysts and reaction partners.

Advantageously, the ash cycle is carried out as a function of the measurand which is affected by the combustion process, the measurand being determined in the flue gas of the combustion plant.

Most simply, the concentration of carbon monoxide or oxygen in the flue gas, excess air from combustion, or the temperature of the combustion chamber can be used as the measurement amount.

In the modern waste incinerator apparatus, the concentration of carbon monoxide in the normal combustion operation is approximately 5-20 mg / m ^3, but if the concentration of carbon monoxide (CO) is 100 mg / m ³ or more, it is considered as a special combustion condition of the present invention. Initiate the intervention from the point of view.

Moreover, it is advantageous to use the oxygen content in the flue gas as one of the measured quantities, especially when the oxygen content drops below 5% by O ₂ capacity in the waste incinerator apparatus, or when excess air is measured, It is advantageous if it falls below 1.4. Similarly, the temperature of the combustion chamber of the combustion plant can be used as one of the measurements when measured at a height of approximately 6-10 meters above the main combustion zone and falls below 800 ° C.

As another embodiment of the invention, it is advantageous that the ash ash circulation can be initiated as a function of organic pollutants, in particular PCDDs and / or PCDFs or their precursors, determined in the flue gas of the combustion plant.

Advantageously, the measurand is determined through on-line analysis of the flue gas.

In particular, the round of rotation is implemented as a function of the predetermined I-TEQ threshold. The threshold defining the specific combustion conditions can be set to be between 0.1 and 5 ng I-TEQ / m ³ in the flue gas.

The measurement is preferentially covered with both gaseous organic and particle-bound organic contaminants, and is carried out at the top of the boiler or in the raw gas on the upstream side of the flue gas treatment apparatus. Suitable analytical methods for this are disclosed in literature such as Resonance Enhanced Multiple Photon Ionisation and Time of Flight Mass Spectrometry (REMPI-TOFMS), for example monochloro Enable direct on-line analysis of benzene. The figures from the experiments showed that monochlorobenzene was highly related to I-TEQ in the flue gas. Thus, the online measuring device may be called a TEQ sensor. However, according to the present invention, sensors for other molecules or other types of molecules can also be used if the signal from this sensor has a unique relationship with the content of harmful organic pollutants in the flue gas.

In another preferred embodiment of the present invention, the non ash cycle is carried out during a particular time period after a particular combustion condition is confirmed. The figures obtained from the experiment play a special role here. For example, the fly ash cycle is carried out in a period of 10 minutes to 6 hours after the specific combustion conditions have been confirmed. The fly ash period can be determined as a function of the measurand level. Here, the measured amount is a measured amount affected by the combustion process, the concentration of carbon monoxide or oxygen in the flue gas, the concentration of excess air from combustion, the temperature of the combustion chamber, or the organic pollutants in the flue gas, in particular PCDDs and And / or the concentration of PCDFs or their precursors.

For the purpose of determining specific combustion conditions, if analytical instruments are used that facilitate the rapid determination of the measurements (as in the case of the measurement techniques and measurments described above), in a more preferred embodiment of the present invention, It is desirable to define the period as a function of the measurement level. Thus, if the predefined threshold is substantially exceeded, the cycle period will be longer than if the threshold was slightly exceeded.

In order to reliably dispose or decompose harmful organic compounds or precursor materials, in another preferred embodiment of the present invention, fly ash is circulated to the main zone of the hot combustion plant.

When a grate-based system is used in the combustion plant, it may be advantageous for the fly ash to be circulated to the fuel bed in the main combustion zone.

In another preferred embodiment, if the cycle of ash ash is carried out after confirmation of a particular combustion condition or during or after boiler cleaning, the aforementioned disadvantageous results, i.e., ash ash remains attached to the boiler tube or contained in ash ash during the operation period. The reactant precursor material can be prevented from reacting with it to form dioxins. Thus, not only fly ashes but also the obtained aggregates are subjected to a cyclic process.

The boiler is cleaned by lapping, brushing, or soot blowing.

The fly ash accumulated in the flue gas treatment device on the downstream side of the steam generator is preferably circulated with the circulated fly ash as described above. This method is carried out when specific combustion conditions are identified.

Circulating fly ash recovered from the filter on the downstream side of the steam generator (boiler) can also be practiced in accordance with the present invention if certain combustion conditions are identified.

Of course, even if the operator of the combustion plant always tries to remove certain combustion conditions again as quickly as possible through an appropriate method, the removal is not carried out automatically, for example by combustion control.

If confusion in the combustion sequence does not occur and no specific combustion conditions are identified, boiler cleaning is performed at normal frequency. In this regard, the interval between the two cleaning steps is mainly set at about 4 hours. As a result, the generated ash is disposed of by the normal disposal route.

Next, one embodiment of the method according to the invention will be described simply and exemplarily according to the flow chart of FIG. 1.

In this embodiment, a combustion operation is performed (step 100), and online gas measurement such as harmful organic pollutants or carbon monoxide is performed (step 102). Alternatively, the representative temperature of the flue gas is measured (same step 102). Thereafter, it is determined whether the fly ash meets the specific condition of circulation (step 104). If a particular combustion condition is identified through an increase in the concentration of organic pollutants or carbon monoxide or a significant deviation in temperature from a set point during the process, the boiler is lapping, brushing, or soot blowing at the point of confirming a predetermined increase or temperature deviation. It is cleaned by (step 106). The fly ash obtained by the cleaning is then circulated to the combustion plant (combustion chamber, combustion chamber) (step 108). If a malfunction is reported, i.e. not meeting specific combustion conditions, normal boiler cleaning is performed at regular intervals (step 110). The fly ash obtained is conveyed out of the process for disposal purposes (step 112 and step 114).

Although the present invention has been described in the embodiments, it is not limited thereto. All modifications, variations, and additions that can be readily made by those skilled in the art are made within the technical aspects of the present invention.

As is evident from the above description, in accordance with the present invention, as much of the precursor material or other organic contaminants as possible are destroyed, thereby minimizing the amount of harmful organic compounds exiting the combustion plant along with the fly ash, thereby minimizing the ash flow to the combustion process. There is provided a method of removing organic pollutants in fly ash that can control.

Claims (16)

A method of removing organic pollutants in fly ash of a combustion plant in which at least a portion of fly ash generated in the furnace is intermittently circulated into the combustion process, Circulating said fly ash while monitoring said organic pollutant as a function of specific combustion conditions. The method of claim 1 wherein the cycle of fly ash is carried out as a function of the measurand influenced by the combustion process determined in the flue gas of the combustion plant. 3. The method for removing organic pollutants in fly ash according to claim 2, wherein the concentration of carbon monoxide or oxygen in the flue gas, excess air from combustion, or the temperature in the combustion chamber of the waste incinerator apparatus is used as the measured amount. 2. The removal of organic pollutants in fly ash according to claim 1, characterized in that the circulation of fly ash is carried out as a function of organic pollutants, in particular PCDDs and / or PCDFs or their precursors, determined in the flue gas of the combustion plant. Way. The method according to any one of claims 1 to 4, wherein the measurand is determined through on-line analysis of flue gas. 5. The method of claim 4 wherein the cycle of fly ash is carried out as a function of a predetermined I-TEQ threshold. 7. The method of claim 6 wherein the I-TEQ threshold is selected between 0.1-5 ng I-TEQ / m ³ in flue gas. 8. A cycle according to claim 1, 2, 3, 4, 6, or 7, wherein said non- ash cycles are carried out during a specified period of time after said particular combustion condition is confirmed. Method of removing organic pollutants in fly ash. 6. The method according to claim 5, wherein the cycle of ash ash is carried out in a period of 10 minutes to 6 hours after the specific combustion condition is confirmed. 8. The non-cyclic cycle period according to claim 1, 2, 3, 4, 6, or 7, as a function of the measurand level measured according to claim 2 or 4. A method for removing organic pollutants in fly ash, characterized by the above-mentioned. 8. Removal of organic pollutants in fly ash according to claim 1, 2, 3, 4, 6, or 7, characterized in that the fly ash in the main temperature range is circulated to the combustion plant. Way. 12. The method of claim 11 wherein the fly ash is circulated to a fuel bed in the main combustion zone when a grate based system is used in the combustion plant. 8. The organic pollution in fly ash according to claim 1, 2, 3, 4, 6, or 7, wherein said fly ash circulation is carried out after said specific combustion condition is confirmed. Method of removal of the substance. The method according to claim 1, 2, 3, 4, 6, or 7, wherein the circulation of fly ash is carried out during or after boiler cleaning. How to remove. 15. The method of claim 14 wherein the boiler cleaning is performed by lapping, brushing, or soot blowing. 14. The removal of organic pollutants in fly ash according to claim 13, wherein the fly ash contained in the flue gas treatment apparatus on the downstream side of the steam generator is accumulated together with the fly ash obtained according to claims 13-15. Way.